In recent years percutaneous transluminal angioplasty has become a common procedure for use in treating an obstruction (stenosis) in an artery. The treatment results in improved blood flow and circulation through the treated artery.
Although the most common type of treatment involves the use of a balloon catheter that is advanced through the patient's arteries into the stenosis and is then expanded under pressure to dilate the stenosis, other techniques for enlarging the stenosed region of the artery are under development.
The term "angioplasty" as used in this specification is intended to mean not only the treatment of stenoses with a balloon catheter but is intended to encompass other modes for treating stenoses such as with laser catheters, atherectomy catheters or the like. When angioplasty is performed on the coronary arteries, the procedure is referred to generally as percutaneous transluminal coronary angioplasty (PTCA). PTCA is an alternative to coronary bypass surgery. The PTCA procedure is of relatively short duration and involves puncturing the skin and an artery (usually the femoral artery in the patient's leg) to provide access to the patient's arterial system for the PTCA catheter. The PTCA catheter is navigated through the patient's arteries until it reaches the coronary artery to be treated. Typically, a patient undergoing PTCA will have a hospital stay of one or two days and will be able to resume full activity shortly thereafter. In contrast, treatment of a stenosed artery by coronary bypass surgery involves a very extensive and expensive operation with a long recuperative period.
In a significant number of angioplasty cases, the region of the artery where the angioplasty was performed may reclose, either as a result of acute closure or as a result of restenosis. Acute closures are vascular emergencies in which the artery collapses during or immediately after the angioplasty procedure. Such events are usually caused by damage to the artery or by a thrombus. Restenosis, on the other hand, occurs at a much later date, usually some weeks or months after the procedure. The restenosis may result from redevelopment of stenotic material (e.g., fatty material, cholesterol deposits, etc.) in the artery or from trauma to the interior surfaces of the artery which occurs during catheter placement or withdrawal. Follow up data for PTCA procedures has indicated that a small percentage of patients develop acute closure within one hour after the PTCA treatment and approximately 30% redevelop a restenosis within six months after the PTCA treatment. This restenosis will require further treatment either by one or more subsequent angioplasty treatments or, possibly, and ultimately by coronary artery bypass surgery.
A number of techniques and devices have been proposed to solve the problem of restenosis. Among them has been to insert a generally tubular element, referred to as a stent, in the artery at the site of the stenosis after the angioplasty is performed. The tubular element is introduced in a low profile condition (e.g., a small effective cross-sectional diameter), is placed in the artery at the region of the angioplasty and is then expanded into engagement with the wall of the artery. For example, U.S. Pat. No. 4,740,207 to Kreamer discloses a generally tubular stent having a spiral cross-section. The stent is delivered to the site of the angioplasty by mounting it on the balloon of a balloon catheter and then advancing the balloon catheter, carrying the stent, into the artery. When the balloon and stent are positioned at the site of the angioplasty, the balloon is inflated to expand the stent into engagement with the artery wall. The stent disclosed in the Kreamer patent incorporates a latching mechanism by which the stent locks in the expanded configuration so that it will be securely retained within the artery. The balloon catheter then may be deflated and removed from the patient. In placing the stent, it is important that the delivery catheter have a low profile, that it hold the stent securely in its collapsed configuration, that it enable easy expansion and release of the stent and that it permits the delivery catheter to be withdrawn. It is among the general objects of the invention to provide such a delivery catheter.